In the 3rd Generation Partnership Project (3GPP), work is ongoing on specifications of the UMTS Terrestrial Radio Access Network (UTRAN) evolution (E-UTRA) as part of the Long Term Evolution (LTE) effort.
Studies show that it is advantageous to schedule Voice over Internet Protocol (VoIP) users based on the time that packets have waited in the scheduler buffers. This is known as delay scheduling. It is well known how to do this in the downlink where the scheduler has access to the transmission buffers.
The radio downlink is the transmission path from a base station, e.g. an eNodeB to a terminal, or a User Equipment (UE) as the terminal also may be referred to as. The uplink is the inverse of a downlink, i.e. the transmission path from the terminal to the base station.
No information about the queuing delay in the terminal is available in the uplink scheduler. This information can however be explicitly signalled from the terminal to the scheduler.
In LTE, scheduling is modelled in the Medium Access Control (MAC) layer and resides in the eNodeB. The scheduler assigns radio resources, also called Resource Blocks (RB), for the downlink (assignments) as well as for the uplink (grants) using the Physical Downlink Control Channel (PDCCH).
For uplink scheduling, the eNodeB needs information about the current state of the buffers in the terminal, i.e. if and how much data the terminal has in its priority queues. This information is sent from the terminal to the eNodeB either as a 1-bit Scheduling Request (SR) or by a Buffer Status Report (BSR). The Scheduling Requests are transmitted on a control channel such as e.g. Physical Uplink Control CHannel (PUCCH) or Radio Access CHannel (RACH) while the BSR are transmitted on the data channel such as e.g. Physical Uplink Shared CHannel (PUSCH), mostly together with user data.
The problem with the existing solution is that explicit signalling of delay information is costly in terms of resource usage, which leads to lower capacity and/or coverage. Also, scheduling principles that do not take delay into account perform worse than ones that do.